1. Field of the Invention
The present invention relates to a full color toner for nonmagnetic one-component development used for development of electrostatic latent images in electrophotography, electrostatic recordings, electrostatic printing, and the like.
2. Discussion of the Related Art
As disclosed in U.S. Pat. Nos. 2,221,776, 2,297,691 and 2,357,809 and other publications, conventional electrophotography utilized in apparatuses for forming fixed images comprises the steps of forming an electrostatic latent image by evenly charging a photoconductive insulating layer (a charging process) and subsequently exposing the layer to eliminate the charge on the exposed portion (an exposing process) and visualizing the formed image by adhering colored charged fine powder known as a toner to the latent image (a developing process); transferring the obtained visible image to an image-receiving sheet such as a transfer paper (a transfer process); and permanently fixing the transferred image by heating, pressure application or other appropriate means of fixing (a fixing process). The above method may further comprise, subsequent to the transferring of the visible image, scraping off residual toners on the photoconductor for the purpose of cleaning the photoconductor surface (a cleaning process).
Among the above electrophographic methods, in the developing process, there have been proposed, as the most convenient method, two-component magnetic brush development methods using a developer consisting of two components, namely, a toner and a carrier, the carrier being used for the purposes of supplying electric charges to the toner and of conveying the charged toner onto the latent image portion by a magnetic force.
However, in the two-component magnetic brush developing method, since a magnetic force is utilized in the conveying of the developer, a magnet has to be placed in the developer roller, and the carrier is made of a metal or an oxide thereof such as iron powder, nickel powder, and ferrite. Therefore, the developer device and the developer become undesirably heavy, thereby making it difficult to miniaturize and thus reduce the weight of the overall recording device.
In addition, as disclosed, for instance, in U.S. Pat. Nos. 3,909,258 and 4,121,931, there have been conventionally well used magnetic one-component development methods comprising the step of conveying a toner to the electrostatic latent image portion without using a carrier, the methods being carried out by utilizing a magnetic force owned by the toner containing a magnetic substance therein. However, a magnet has to be also used in the inner portion of the developer roll in this development method, making it disadvantageous from the aspect of reducing the weight of the developer device.
In order to solve the problems in these development methods, much studies have been recently conducted and much improvements made on nonmagnetic one-component development methods wherein a toner alone is used without containing any magnetic powder, as disclosed, for instance, in U.S. Pat. Nos. 2,895,847 and 3,152,012, and Japanese Patent Examined Publication Nos. 41-9475, 45-2877 and 54-3624. These development methods are extremely advantageous for miniaturizing and reducing the weight of the recording device from the aspect of using no magnets in the developer roller. Particularly, there are an increased number of cases of using the above development method for such applications as miniaturized printers for personal computers and plain paper facsimiles in which much studies and development have been actively made in the recent years.
However, since the nonmagnetic one-component development method does not utilize a carrier, extremely large difficulty is posed in controlling the amount of the triboelectric charges of the toners. Also, particularly in the case of a full color toner, only colorless charge control agent can be used, thereby making it difficult to maintain good triboelectric chargeability.
Therefore, in order to maintain stable triboelectric chargeability, color toners for nonmagnetic one-component development containing chargeable colorant-containing fine particles and organic fine resinous particles being reversely chargeable thereto when subjecting to triboelectric charging with an iron powder are disclosed, for instance, in Japanese Patent Laid-Open Nos. 3-296771, 4-9865, and 4-19754. However, these toners have problems in that the fine resinous particles are likely to be fused to the charger blade or that the fine resinous particles are likely to form filming on the photoconductor.
Also, Japanese Patent Laid-Open No. 7-27087 discloses a toner to which a silica being subjected to a hydrophobic treatment with a silicone oil is applied in order to obtain a toner with excellent developability, transferability, and stability with a passage of time. However, this toner contributes little to the triboelectric chargeability of the toner, thereby making it difficult to use such a toner in cases of high-performance devices where extremely rapid initial rise in the amount of the triboelectric charges is in demand from the aspects of the level of background and the image quality.
Accordingly, an object of the present invention is to provide a full color toner for nonmagnetic one-component development having excellent triboelectric chargeability.
These and other objects of the present invention will be apparent from the following description.